MOSCOW, April 28 (Reuters) - The United States on Monday imposed visa bans and asset freezes on seven Russian officials close to President Vladimir Putin and put sanctions on 17 companies, saying Moscow had failed to abide by an agreement to defuse the crisis in Ukraine.

Here is information about the individuals targeted:

* Igor Sechin, 53, heads state-controlled Rosneft, Russia's biggest oil producer. A powerful, longtime Putin ally and former Kremlin deputy chief of staff who for years wielded his influence from the shadows, he is the most senior energy executive targeted by the sanctions.

* Dmitry Kozak, 55, is a deputy prime minister with responsibility for overseeing the integration of Crimea into Russia following its annexation from Ukraine. He won Putin's trust since working with him in the St. Petersburg city administration in the 1990s and oversaw the organisation of the Winter Olympics in Sochi.

* Vyacheslav Volodin, 50, a wealthy former lawyer and veteran political strategist, is Putin's deputy chief of staff. Critics say he is the mastermind behind Putin's conservative stance and what they see as a clampdown on dissent during his third term, both meant to tighten the president's grip on power after street protests in 2011-2012.

* Sergei Chemezov, 61, heads Rostec, a conglomerate formed by Putin in 2007 by uniting more than 600 companies that make products including weapons and automobiles and which employs close to a million Russians. In the 1980s, he served in Soviet intelligence in what was then East Germany, along with Putin.

* Alexei Pushkov, 59, is head of the lower chamber of parliament's international affairs committee. An anchor of a long-running current affairs programme on Russian television, he has often criticised U.S. policy. Pushkov has aligned himself closely with the Kremlin's policy on the United States, including a ban on U.S. adoptions of Russian orphans as well as on policies on Syria and Ukraine.

* Oleg Belaventsev, 64, was appointed Putin's envoy to Crimea on March 21, the day Russia formally incorporated the Black Sea peninsula. A vice-admiral, he is close to Sergei Shoigu, Russia's defence minister and another longstanding Putin loyalist, according to Russian media.

* Yevgeny Murov, 68, has been the head of a state security agency that protects senior state officials, the FSO, since 2000. A general, he worked for the KGB for nearly 20 years until the fall of the Soviet Union in 1991, and in its main domestic successor, the FSB, afterwards. (Compiled by Gabriela Baczynska; Editing by Robin Pomeroy)